As per our Android Integration Guide, your FCM Sender ID should be specified in the AndroidManifest.xml file of your app.
However, it could also have been fetched from google-services.json file sometimes.
If you have many different projects for your apps a mismatch between the data in AndroidManifest and google-services.json can easily happen.
A mismatch of this nature will lead to the "Invalid registration" error report in your Push History and invalidation of your user base!
We deployed a fix for this in Android SDK 5.7.2 that allows SDK to ignore the information in google-services.json, and explicitly use the one from AndroidManifest.
Please make sure that SenderID you specify in AndroidManifest matches the one in the Pushwoosh Contol Panel to avoid any issues!